Optimal water, nitrogen use in almonds

Preliminary results of a multidisciplinary research study aimed at optimizing water and nitrogen use in almonds and other nut crops are already yielding important information related to environmental stewardship and offer the potential for novel management of these two key inputs.

The study integrates a number of institutions, including UC and NASA. It also includes numerous experts in plant sciences, land, air and water resources, engineering, and remote sensing. This work was initiated with funding by the Almond Board and others and now is substantially leveraged by farm bill grant funds.

One key finding reported by Dr. David Smart (UC Davis Viticulture and Enology) and Blake Sanden (UC Cooperative Extension, Kern County) at the 2009 Almond Industry Conference is that the current practice of micro-irrigation combined with fertigation can yield 70 percent to 80 percent nitrogen use efficiency (NUE), which is among the most efficient ever measured in agriculture. NUE is calculated as the nitrogen applied vs. nitrogen removed with the crop.

The test orchard yielded 3200-3400 kernel pounds per acre and received 53 inches of water in season. This NUE was obtained by applying total N in the range of 250-275 pounds per acre through microsprinklers or drip, making several applications of 25 to 60 pounds each in February, March, April, May and June to match demand during growth and fruit development. This high efficiency approach matching in-season demand has led to low off target movement of N. Soil monitoring of the test orchard revealed nitrates did not move out below the root zone, while air monitoring showed off-gassing of nitrous oxide (N2O) is much less than originally estimated. N2O is one of three major greenhouse gases.

This research also is helping to develop new tools to manage water and nutrients, such as remote sensing (e.g., aerial over-flights and satellites) combined with ground-level sensing. Sensing leaf temperature using infrared (IR) sensors is showing potential as a tool for irrigation management by determining plant water status. Using pressure chambers to measure leaf stem water potential is the current standard, but this technique is time-consuming and is based on single tree/leaf readings. Mounting IR and other sensors on a mobile platform to detect water status and tree stress could provide a more rapid and comprehensive orchard assessment. To this end, UC Davis pomologists and ag engineers Drs. Bruce Lampinen, Shrini Upadhyaya and David Slaughter have mounted this suite of sensors to assess water status on a Kawasaki Mule, which is then driven through the orchard. A light bar mounted on the Mule has successfully measured light interception and the corresponding yield across orchards of varying age and condition. This has been a valuable research tool for assessing yields in trials, and could become an important production tool in the future.